Goods such as perishable food items that must be kept within certain temperature ranges during transfer between locations are transported in vehicles such as trucks, trailers, rail cars, or refrigerated containers provided with a refrigeration system that interfaces with the cargo space to maintain the cargo at a predetermined temperature. The refrigeration system may include a transport refrigeration unit capable of producing cold or warm air and transferring the air into the cargo space. In basic implementations, the transport refrigeration unit may be controlled by a thermostat that monitors the temperature of the cargo space and alternately turns the unit on and off to maintain a preset temperature. In modern implementations, however, more sophisticated control devices and graphical user interfaces are integrated into the transport refrigeration unit and may be capable of providing more intelligent control of the unit. These control devices may monitor operating parameters of the refrigeration unit and the cargo area of the vehicle, and then control the unit based on the collected data to efficiently maintain the specified temperature of the cargo area and adjust for changes in the operating conditions affecting the temperature within the cargo space.
The control device or main module is typically mounted on the refrigeration unit, and may include a graphical user interface having a display screen and input devices, such as buttons, that allow a user to view information stored at the control device, to change settings for the refrigeration unit, and to navigate through a system of menus to get to the desired information and to cause functions to be executed by the control device to control the operation of the refrigeration unit. Currently, a visual output device, such as dot matrix or similar type of display, may display the available menus to a user, but menus are typically difficult to traverse and manage, and take time to navigate to the desired function or data. Consequently, it is desirable to provide a control device having input devices and displays allowing a user to quickly and intuitively navigate menus and display desired data and control functionality.
Another issue with control devices for the transport refrigeration units in current use is the general availability of the entire menu system to virtually anyone that can operate the inputs of the control device. With many current control devices, any person could walk up to the refrigeration unit when the vehicle is parked at a truck stop, press the buttons on the control device, and view information contained therein and possibly alter settings of the graphical user interface. Certain information available at the control device is important for the driver of the vehicle to know the current conditions within the cargo space and whether the refrigeration unit is operating properly. However, the owners of the vehicles may wish to limit the amount of information and menus available to drivers, and the amount of data to which the drivers have access, either for security reasons or because such information is wholly irrelevant to the driver's task of transporting the shipment to its destination. Therefore, a further need exists to lock the driver out of certain menus while allowing other authorized users of the control device to freely navigate the menus to which they are granted access.